This invention relates to glass fiber-reinforced plastic compositions.
Vinylized epoxy resins, such as vinyl ester or unsaturated polyester resins comprise a well known class of thermosettable polymers. When formulated as fiber-reinforced plastic structures, they are used in corrosion-resistant applications. Typical formulations comprising vinyl ester resins include plastic composite sheet molding compounds, resin transfer moldings and hand layups. For example, such resins are dissolved in a solvent or reactive diluent such as styrene, reinforced if desired, to obtain greater strength and modulus, applied to a substrate; and cured.
Vinyl ester or unsaturated polyester resins are typically prepared by reacting an unsaturated monocarboxylic acid with an epoxy resin such that a resin containing the characteristic vinyl ester moiety is provided. The physical properties of the vinyl ester resins will typically depend upon factors such as the epoxy reactants and the copolymerizable monomers which are employed. Additionally, certain inert reinforcing agents can be employed.
Vinylized epoxy plastics can be reinforced with glass fibers. Such fibers provide structural stability and electrical insulative properties to the plastics. These plastics find many uses, especially in the construction industry.
Typically, the glass fibers are treated with an organosilane coupling or sizing composition to facilitate its compatibility with the resin. The adhesion of resin and glass is improved and the glass is protected from abrasion during its production, shipping, and eventual use. These sizings have been selected such that the organic portion of the sizing will be partially soluble in and react with the resins.
Unfortunately, it has been observed that vinylized epoxy resins reinforced with sized glass fibers can display fiber prominence or a weakening at areas of high stress when cured using a metal composition. Typically, fiber prominence has been observed when sized glass fibers are used to reinforce vinyl ester or unsaturated polyester resins which have been diluted to a slightly acidic or basic pH, for example in styrene diluted resins. The phenomenon especially occurs when the resin has a pH greater than about 5.7 measured as a 10 percent methanol solution.
Therefore, it would be desirable to provide a composition and a method for preparing glass fiber-reinforced vinylized epoxy resins, which when cured using a metal composition, will display reduced fiber prominence.